The present invention relates to a method for underwater ranging with sound pulses, particularly for the detection and/or classification of objects at or near the bottom of a water body.
In a known sonar device operating according to this method, the so-called lateral sight sonar, a transmitting transducer and a direction selective receiving device are arranged on a single marine vessel and both directional characteristics are oriented essentially transversely to the direction of travel of the vessel. The transmitting transducer emits sound over a relatively broad transmitting area transversely to the direction of travel of the vessel. The receiving device, which includes a receiving transducer whose length is substantially greater than that of the transmitting transducer, simultaneously covers a plurality of strip-shaped receiving regions lying within the transmitting area.
With such a sonar device, a relatively high rate of advance can be realized for the vessel and thus a high search and sweep output.
The quality of the solution, however, depends on the azimuthal width of the receiving regions, i.e. on the aperture angle of the receiving sectors emanating from the receiving transducer, such that the smaller the receiving sector, the higher the resolution quality. The rate of advance, however, depends on the aperture angle of the transmitted beam leaving the transmitting transducer and is directly proportional thereto. Since the entire transmitting area must be covered by the receiving sectors, a very large number of extremely narrow receiving sectors is required to obtain a useful resolution. This places very high demands on the receiving transducer as well as on the signal processing required for forming the receiving sectors, i.e. the receiving beams. The latter requires quite a considerable amount of computer capacity and a large amount of hardware.
Such a known sonar device, moreover, can be used only conditionally for the purpose of mine detection since the direction of detection being exclusively to the side of the direction of travel, the vessel carrying this sonar device may inadvertently enter a mine field and is thus always very much in danger. For purposes of mine detection, such sonar devices are therefore installed only on unmanned, or drone, ships and a second guide ship is required which accompanies the drone ship at a safe distance. Nevertheless, because of the high mechanical and electronic investment in the drone ship, the high risk of its loss is objectionable.